The invention relates to a method and apparatus for providing a timing signal to indicate the timing of an engine and, more particularly, to a method and apparatus for producing an engine timing signal for diesel engines having a fuel injection system.
In order to assure optimum operation of an internal combustion engine, service procedures are periodically practiced whereby, for example, the engine timing is set to an appropriate value. Engine timing for a spark ignition internal combustion engine is relatively simply adjusted since an electrical signal providing timing information is easily obtainable from the distributor. However, in diesel engines there is no such electrical signal available because of the absence of spark plugs and a distributor; consequently, other techniques are employed for timing purposes.
With a diesel engine having a fuel injection system, injection occurs when the fuel pressure is at a predetermined value such as 1000 psi. Typically, fuel pressure in the fuel line leading to one of the diesel engine cylinders is sensed by a pressure transducer for developing a timing signal when the fuel pressure reaches the predetermined value. At this moment of fuel pressure, the fuel injector is activated to inject fuel into the corresponding cylinder.
One diesel engine timing technique requires breaking into and modifying the fuel line to accommodate a transducer which must be in direct communication with the fuel to tune the engine. This is not desirable since it takes a relatively long period of time to open the fuel line connection, insert the transducer to adjust the timing, close the connection, and then remove the transducer from the fuel line after tuning the engine. Furthermore, since diesel engine fuel lines are under high pressure, the connections must be carefully opened and closed.
In another technique, the above disadvantages have been substantially eliminated by employing a transducer which has a detector mounted on the outside of the fuel line such that expansion and contraction of the line causes variations in the transducer output. This pressure transducer can be of the strain gauge type having at least one resistance element mounted directly on the fuel line circumference. Piezoelectric devices or other clamp-on types of pressure transducers can also be used. A disadvantage with such externally located transducers is that it has not yet been possible to calibrate the transducer for proper correction factors to account for inaccuracies in its output. The measured output signal is inaccurate because variation in fuel line wall thickness and other factors will affect transducer sensitivity. It is therefore desirable to utilize such an externally mounted type of pressure transducer, but without engine timing errors produced by transducer inaccuracies.